1. Field of the Invention
The present invention relates to the technical field of devices designed to emit pulsed laser beams for use in the medical field in a broad sense.
In the medical field, lasers are used mainly either for incision or cutting purposes analogous to a scalpel, or else for coagulating or cauterizing human tissue.
2. Description of Related Art
Thus, it is known to make use of a neodymium-doped Nd YAG laser at a wavelength of 1.06 .mu.m. The light radiation is absorbed by tissue and enables the tissue to be heated, and the associated cauterizing effect to be obtained. At this wavelength, the laser beam is transmitted by a silica optical fiber which enables it to be used inside the body without requiring a surgical opening. Pulsed operation makes it possible to drill and abrade hard tissue. Nevertheless, cutting soft tissue is lengthy and the cut is broad, with too deep a zone being affected thermally.
It is also known to use a CO.sub.2 laser beam which enables tissue to be vaporized, such that the focused beam cuts into the surface and makes an incision. Such a beam which operates at a wavelength of about 10 .mu.m is highly absorbed by tissue. Soft tissue is cut well. However, hard tissue is sometimes cracked by thermo-diffusion of the laser. Also, the CO.sub.2 laser beam does not propagate along flexible optical fibers, so the beam needs to be fed by means of a relatively complex combination of tubes and mirrors.
In order to combine the advantages of both of the above lasers, proposals have been made to implement a device integrating two lasers of the above types. Nevertheless, it must be understood that the CO.sub.2 laser retains its drawbacks, thereby considerably restricting the field in which such a device can be applied.
French patent application FR 2 607 329 proposes an Nd YAG laser fitted with beam wavelength selection means for selecting a value of 1.44 .mu.m. At that wavelength, light is better absorbed by the water contained in tissue than is light at a shorter wavelength, e.g. equal to 1.32 .mu.m or to 1.06 .mu.m, which are the other transition values of an Nd YAG laser.
When a powerful laser beam at the wavelength of 1.44 .mu.m is, focused on tissue, the surface of the tissue is heated and evaporates in a manner that is substantially identical to using a CO.sub.2 laser beam, thus providing an incision in the tissue. The major drawback of that laser device lies in its low efficiency, requiring the use of overdimensioned excitation and cooling means in order to obtain laser power that is sufficient for most of the intended applications. The resulting prohibitive cost has restricted the spread of that laser device.
The Applicant has examined numerous prior art solutions and has thus found that there does not exist any multipurpose lasers providing a beam that can be transmitted by optical fibers.
The Applicant thus has the merit of drawing up a list of characteristics that ought to be found in a laser device for medical use, in order to satisfy user needs. It has thus been observed that the laser beam needs to possess a wavelength that is suitable for being absorbed both by hard tissue and by soft tissue, so as to make it possible both to cut and coagulate soft tissue and to remove hard tissue. The term "soft tissue" is used, for example, to cover mucous membranes, gums, dental pulp, parenchyma, muscles, or tumors, while the term "hard tissue" is used to cover, for example, enamel, dentine, calculi, bone, cartilage, or atherosclerosis.
Additionally, a laser beam at such a wavelength must be capable of propagating along a flexible optical fiber so as to be suitable for inserting inside hollow organs, and more generally, the human or animal body. Also, such a device should be compact and easy to use.
In numerous applications, a laser device must deliver power in the range 2 watts to 20 watts. To deliver such power, a laser device must have good efficiency so as to avoid using excitation means and consequently cooling means that are too powerful, which increases in prohibitive manner both the size and the cost of manufacturing such a laser, thus making it inaccessible in numerous applications.
The Applicant has thus shown that there exists a need for a laser device capable of cutting soft tissue and of ablating hard tissue, providing a beam that is suitable for being conveyed by means of a flexible optical fiber, and that is of an efficiency that is suitable for enabling it to be implemented at an acceptable cost in the numerous uses for which the device is intended.
After specifying the above need, the Applicant has developed a laser device that satisfies the set of technical characteristics required in the various applications envisaged.